Sen. Joseph Lieberman

The battle to end Washington, D.C.’s controversial school voucher program is entering a critical phase.

A little background: The plan, pitched as an “experiment,” was initially authorized in 2004 for five years. Heavily promoted by the Bush administration, it passed the House of Representatives by a single vote six years ago on a night when many voucher opponents were away from the floor. Republicans held the vote open for more than 40 minutes to gather the necessary votes. It later cleared the Senate only as a result of a procedural move.